Output location in an array

[Gactimus]

I made the program below. It outputs the smallest number in the array. What
I would like to know is how do I output the array location. I am at a loss.

For example, since the smallest number in the array is 2, the output should
be 2 for the number and 1 for the location. If anyone could help or point
me in the right direction that would be great. Thanks.


-------------------
#include <iostream>
using namespace std;

int main()
{

int array[3];

array[0] = 5;
array[1] = 2;
array[2] = 10;

int k = 0;
for (int i = 0; i < 3; i++)
if (array < array[i+1])
k = i;

cout << k;


return 0;
}

 

[Vyacheslav Kononenko]

I made the program below. It outputs the smallest number in the array. It does not
What
I would like to know is how do I output the array location. I am at a loss.

You need to fix your program then it should be clear for you.

For example, since the smallest number in the array is 2, the output should
be 2 for the number and 1 for the location. If anyone could help or point
me in the right direction that would be great. Thanks.

I think right direction is to think before you program, sorry.

[skip]

 

[Howard]

I made the program below. It outputs the smallest number in the array. What
I would like to know is how do I output the array location. I am at a
loss.

For example, since the smallest number in the array is 2, the output
should
be 2 for the number and 1 for the location. If anyone could help or point
me in the right direction that would be great. Thanks.


-------------------
#include <iostream>
using namespace std;

int main()
{

int array[3];

array[0] = 5;
array[1] = 2;
array[2] = 10;

int k = 0;
for (int i = 0; i < 3; i++)
if (array < array[i+1])
k = i;

cout << k;


return 0;
}

That's likely to crash! The if statement compares against array[i+1], and
when i equals 2, it will try to access array[3], which is illegal (undefined
behavior).

Let's look at what your code actualy does. You say it reports the smallest
number, but it doesn't. The variable k gets the value of i, which is the
index ("location", in your terms), not the value from the array. To get the
value, you need to set some variable equal to array. You can do that in
a second variable, named min, for instance. In that case, the if statement
needs {} brackets, with two assignments inside it: one to assign i to k, and
one to assign array to min.

Now that you have a min variable, use that to compare the current array
value against it, instead of comparing it against array[i+1]. For example,
your if statement could be "if (array < min)".

Of course, you need to have a starting value for min. One convenient
starting value would be array[0], especially since you're already defaulting
k to 0.

Once you do that, your can optimize the loop a little, by startng at 1
isntead of 0 (since you already have k set to 0 and min set to array[0]).
So your for loop goes "for (int i = 1; i < 3; ++i)".

(Get into the practice of using ++i instead of i++. It's not important
here, but may be in later work, and it's a good habit to develop.)

So what's that look like now?

int k = 0;
int min = array[0];
for (int i = 1; i < 3; ++i)
{
if (array < min)
{
k = i;
min = array;
}
}
cout << "min is " << min << " at index " << k << "\n";

(You probably should also get in the habit of using constant variables for
things like the array size, instead of explicit constants like "3" in the
for loop. That way, you can change the array size in just one place and
have al code that refers to the array size changed at once.)

-Howard

 

[Gactimus]

It does not

You're right. It seemed like it worked the first time but when I changed the
numbers around I realized it was wrong.

 

[DaKoadMunky]

int k = 0;

int min = array[0];
for (int i = 1; i < 3; ++i)
{
if (array < min)
{
k = i;
min = array;
}
}
cout << "min is " << min << " at index " << k << "\n";

Is variable min necessary?

It seems that keep tracking of the index would be sufficient. At any given
time the minimum value thus far could be retrieved from the array.

Just curious.

 

[Vyacheslav Kononenko]

I made the program below. It outputs the smallest number in the array. What
I would like to know is how do I output the array location. I am at a
loss.

For example, since the smallest number in the array is 2, the output
should
be 2 for the number and 1 for the location. If anyone could help or point
me in the right direction that would be great. Thanks.


-------------------
#include <iostream>
using namespace std;

int main()
{

int array[3];

array[0] = 5;
array[1] = 2;
array[2] = 10;

int k = 0;
for (int i = 0; i < 3; i++)
if (array < array[i+1])
k = i;

cout << k;


return 0;
}

That's likely to crash! The if statement compares against array[i+1], and
when i equals 2, it will try to access array[3], which is illegal (undefined
behavior).

Let's look at what your code actualy does. You say it reports the smallest
number, but it doesn't. The variable k gets the value of i, which is the
index ("location", in your terms), not the value from the array. To get the
value, you need to set some variable equal to array. You can do that in
a second variable, named min, for instance. In that case, the if statement
needs {} brackets, with two assignments inside it: one to assign i to k, and
one to assign array to min.

Now that you have a min variable, use that to compare the current array
value against it, instead of comparing it against array[i+1]. For example,
your if statement could be "if (array < min)".

Of course, you need to have a starting value for min. One convenient
starting value would be array[0], especially since you're already defaulting
k to 0.

Once you do that, your can optimize the loop a little, by startng at 1
isntead of 0 (since you already have k set to 0 and min set to array[0]).
So your for loop goes "for (int i = 1; i < 3; ++i)".

(Get into the practice of using ++i instead of i++. It's not important
here, but may be in later work, and it's a good habit to develop.)

So what's that look like now?

int k = 0;
int min = array[0];
for (int i = 1; i < 3; ++i)
{
if (array < min)
{
k = i;
min = array;
}
}
cout << "min is " << min << " at index " << k << "\n";

(You probably should also get in the habit of using constant variables for
things like the array size, instead of explicit constants like "3" in the
for loop. That way, you can change the array size in just one place and
have al code that refers to the array size changed at once.)

-Howard

Do you really think that to post the full answer here will help him
learn programming? Especially with an extra variable that is completly
unnecessary:

int k = 0;
for (int i = 1; i < 3; ++i)
if (array < array[k])
k = i;

cout << "min is " << array[k] << " at index " << k << "\n";

 

[chris]

int k = 0;
int min = array[0];
for (int i = 1; i < 3; ++i)
{
if (array < min)
{
k = i;
min = array;
}
}
cout << "min is " << min << " at index " << k << "\n";

Is variable min necessary?

It seems that keep tracking of the index would be sufficient. At any given
time the minimum value thus far could be retrieved from the array.

Just curious.

I was curious too

It was possible that this could be an optimisation (although it would be
a micro-optimisation). However g++ seems to produce virtually identical
code if it is there or not.

Chris

 

[Howard]

Do you really think that to post the full answer here will help him learn
programming? Especially with an extra variable that is completly
unnecessary:

int k = 0;
for (int i = 1; i < 3; ++i)
if (array < array[k])
k = i;

cout << "min is " << array[k] << " at index " << k << "\n";

You're correct, the extra variable isn't needed here. It doesn't make it
wrong or even bad form, though. He might want that information later. It's
simply old habit that I keep important information in an identifiable
variable instead of requiring a "lookup" to get it later. Call it
"pre-emptive optimization".

As for posting the whole answer, yes, I *do* think it helped, in this case.
He tried something, and it was wrong. By the time I'd explained the
problems and potential solutions, in prose, I was afraid he'd just be even
more confused if it wasn't put back together as real code. I walked him
through each step of the corrections, and guided him to the final result.
So, yes, I think it was very helpful.

-Howard

 

[Vyacheslav Kononenko]

Do you really think that to post the full answer here will help him
learn programming? Especially with an extra variable that is completly
unnecessary:

int k = 0;
for (int i = 1; i < 3; ++i)
if (array < array[k])
k = i;

cout << "min is " << array[k] << " at index " << k << "\n";

You're correct, the extra variable isn't needed here. It doesn't make
it wrong or even bad form, though. He might want that information
later. It's simply old habit that I keep important information in an
identifiable variable instead of requiring a "lookup" to get it later.
Call it "pre-emptive optimization".

As for posting the whole answer, yes, I *do* think it helped, in this
case. He tried something, and it was wrong. By the time I'd explained
the problems and potential solutions, in prose, I was afraid he'd just
be even more confused if it wasn't put back together as real code. I
walked him through each step of the corrections, and guided him to the
final result. So, yes, I think it was very helpful.

Okay, I appreciate all your help so far but I still haven't finished the
program. The goal of the program is to to pass an array to a function, get
two values of which I explained earlier, put those values in a structure
and then return the single structure item with the two imbedded values.
After working on it for the last few hours, I have gotten the program down
to one error but I am stuck. Any help would be great.

Here is my code:

-------------------
#include <iostream>
using namespace std;

struct minimum
{
int lowest;
int index;
};

const minimum array[] = {5,9,6,3,2,10};
minimum function(int array[]);
void output(minimum t);


int main()
{
minimum pass = function(array);
output(pass);

return 0;
}

minimum function(int array[])

you should pass size of the array as a second parameter otherway your
function is rather useless(unless your task is define a function that
finds minimum and index of array THAT HAS 7 elements):
minimum function(int array[], int size)

and call will be then
minimum pass = function(array, sizeof(array)/sizeof(array[0]));

{
minimum total;
int k = 0;
int min = array[0];

It is not a mistake but you already have "total" why not to use it
instead of "k" and "min"?

for (int i = 1; i < 7; ++i) for(int i = 1; i < size; ++i)
{
if (array < min)
{
k = i;
min = array;
}
}

total.index = k;
total.lowest = min;

you will not need this two statements if you use total before.